One common application for thermal sensors is in thermal (infrared) detection devices such as night vision equipment. One such class of thermal detection devices includes a focal plane array of infrared detector elements or thermal sensors coupled to an integrated circuit substrate with a corresponding array of contact pads between the focal plane array and the integrated circuit substrate. The thermal sensors define the respective picture elements or pixels of the resulting thermal image.
One type of thermal sensor includes a pyroelectric element formed from a pyroelectric material, such as barium strontium titanate (BST), that exhibits a state of electrical polarization dependent upon temperature changes in response to thermal radiation. For one such thermal sensor, an infrared absorber and common electrode assembly is disposed on one side of the associated pyroelectric element. A sensor signal electrode is disposed on the opposite of the pyroelectric element. The infrared absorber and common electrode assembly typically extends across the surface of the focal plane array and is coupled to the pyroelectric element of each thermal sensor in the focal plane array. Each pyroelectric element has its own separate sensor signal electrode. Each infrared detector element or thermal sensor is defined, in part, by the infrared absorber and common electrode assembly and a respective sensor signal electrode, which constitute capacitive plates, and a respective pyroelectric element, which constitutes a dielectric disposed between the capacitive plates.
To maximize thermal response and enhance thermal image accuracy, each pyroelectric element of the focal plane array is preferably isolated thermally from the associated integrated circuit substrate to insure that the sensor signal from each thermal sensor accurately represents incident infrared radiation. Thermal isolation structures are typically disposed between the focal plane array and the integrated circuit substrate to provide both mechanical support and a sensor signal flowpath, while minimizing thermal coupling between the thermal sensors and the integrated circuit substrate. Several approaches have been used to provide a thermal isolation structure between-thermal sensors and an underlying integrated circuit substrate.